1. Field of the Invention
The present invention relates to a photoelectric converter that converts optical energy to electric energy and a manufacturing method thereof, and a photoelectric conversion module.
2. Description of the Related Art
In a photoelectric converter that converts optical energy to electric energy, in order to increase its photoelectric conversion efficiency, there has been known a stacked thin-film solar battery in which a plurality of thin-film photoelectric conversion layers each having different light-absorbing wavelength characteristics are stacked. In such a conventional stacked thin-film solar battery, a plurality of photoelectric conversion elements are stacked, which respectively include a photoelectric conversion layer in which thin-film semiconductors are deposited in an order of a p-type layer, an i-type layer, and an n-type layer, for example, on an insulating transparent substrate on which a transparent electrode is formed. A reflective conductive film is then formed as a backside electrode, thereby generating photovoltaic power by incidence of light from a side of the insulating transparent substrate.
To smoothly transmit an electric current between stacked photoelectric conversion elements, an intermediate layer having an electrical conductivity is inserted between these photoelectric conversion elements. As the intermediate layer, a material having an optical property that reflects or transmits light in a specific wavelength range can be used. For example, in a GaAs compound semiconductor, as disclosed in Japanese Patent Application Laid-open No. H06-061513, a low resistance structure using a tunnel junction by a high electron-concentration n-layer with a wide bandgap and a high hole-concentration p-layer has been known as the intermediate layer.
Meanwhile, in Si photoelectric conversion elements that are most common in general households, no intermediate layer using such a wide bandgap tunnel junction is used. As a type of the Si photoelectric conversion elements, Japanese Patent Application Laid-open No. 2006-120747 discloses that ZnO, ITO, or SnO2 of n-type transparent conductive oxide (TCO) can be used as a material of the intermediate layer.
In the technique disclosed in Japanese Patent Application Laid-open No. 2006-120747, in the junction with n-type Si, n-types are joined together, and thus a low resistance can be easily achieved. However, in the junction with p-type Si, the junction becomes an n-p junction, and thus a low resistance can be hardly achieved. Therefore, even if a conductive film made of these materials is used, particularly when an electric current generated by the photoelectric conversion layer that concentrates light to generate power is large, the conductivity of the electric current is restricted by the resistance of the intermediate layer, thereby causing a problem such that the photoelectric conversion efficiency of the photoelectric converter is degraded.